how to know which button clicked in javascript

JavaScript
<!DOCTYPE HTML>  
<html>  
    <head>  
        <title>  
            Get the ID of the clicked button 
            using JavaScript 
        </title> 
    </head>  
      
    <body style = "text-align:center;">  
      
        <h1 style = "color:green;" >  
            GeeksForGeeks  
        </h1> 
  
        <p id = "GFG_UP" style =  
            "font-size: 15px; font-weight: bold;"> 
        </p> 
          
        <button id="1" onClick="GFG_click(this.id)"> 
            Button1 
        </button> 
          
        <button id="2" onClick="GFG_click(this.id)"> 
            Button2 
        </button> 
          
        <button id="3" onClick="GFG_click(this.id)"> 
            Button3 
        </button> 
  
        <p id = "GFG_DOWN" style =  
            "color:green; font-size: 20px; font-weight: bold;"> 
        </p> 
          
        <script> 
            var el_up = document.getElementById("GFG_UP"); 
            var el_down = document.getElementById("GFG_DOWN"); 
            el_up.innerHTML = "Click on button to get ID"; 
          
            function GFG_click(clicked) { 
                el_down.innerHTML = "ID = "+clicked; 
            }          
        </script>  
    </body>  
</html>                    
Source

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